Comparing fixed-vessel and moving-vessel ADCP measurements in a large laboratory flume

The error of the spatiotemporally averaged (STA) velocities of moving-vessel (MV) acoustic Doppler current profiler (ADCP) measurements was estimated by comparison with time-averaged fixed-vessel (FV) ADCP measurements in a large laboratory flume. Controlled laboratory conditions ensured that only the movement of the ADCP differed between these two measurements. Three different MV speeds (surrogates of horizontal bin sizes), were investigated. Results indicate no statistically significant differences in the zero-order quantities, discharge, and bulk velocity among STA MV measurements, and between STA MV and FV measurements. However, the traverse speed does affect the accuracy of the measurement of the local velocity, a first-order quantity, including the transverse and vertical components needed to evaluate the turbulence-driven secondary flow in the channel. Although the present study is limited to a unique ADCP, it demonstrates the value of controlled laboratory experiments for quantifying STA MV errors.